1. Field of the invention
The invention relates to a method of manufacturing parts made of a composite material having a metallic matrix.
In the aeronautics industry, and particularly in the construction of aircraft engines, it has long been known to use composite materials comprising reinforcing fibres in a metallic matrix. The advantage of such materials is that they provide tensile strength properties which are enhanced, in proportion to the law of mixtures of fibres and matrix, compared with non-reinforced metallic alloy. This is demonstrated particularly by P. R. SMITH and F. H. FROES in their article published in the JOURNAL OF METALS of March 1984 (19-26), in the case of composites comprising a titanium matrix and silicon carbide fibres. Furthermore, such metallic matrix composite materials, particularly if the matrix is fragile as is the case when it consists for example of a specific compound having an ordered structure such as TiAl or Ti.sub.3 Al, require more work to break the material, in so far as breakage progresses partially by shearing along the interface between the fibres and the matrix, as shown by M. LANCIN in JOURNAL DE PHYSIQUE III (1991 - No. 6 - 1141 to 1166). This increase in breaking stress results in fact from the exposure of consecutive fibres to the propagation of the breakage by decohesion of the fibre/matrix interface between the rupture planes of each of the fibres.
S. J. WANG et al have, in the article published under FATIGUE FRACT. ENG. MAT. STRUC. Vol. 14 No. 4-1991 (391-403), demonstrated that when the fibres are regularly distributed throughout the matrix, rupture under traction parallel to the fibres of a composite material having a metallic matrix with a uni-directional fibre reinforcement is propagated from one fibre rupture plane to another by this mode of shearing of the fibre/matrix interface, but that when the volumetric fraction is locally higher than the average, the fibre adjacent a broken fibre is, in the vicinity of the rupture plane, subjected to a concentration of stress which encourages rupture of the latter in the same plane as before and, by degrees, a plane rupture is observed which is associated with a small amount of work by the traction forces.
2. Summary of the Prior Art
The techniques currently employed in order to produce large size axi-symmetrical parts from a composite having a titanium or titanium-based alloy matrix reinforced by silicon carbide fibres are disclosed in French Patent No. 2 289 425 in the name of SNECMA and in French Patent No. 2 366 904 in the name of ARMINES.
A first method consists of winding onto a former the fibre which is to constitute the reinforcement, so that it forms a layer on the former, and then making a plasma deposition of the material which is to constitute the matrix on the said fibre layer. These two stages of winding and plasma deposition are then repeated as many times as required, and the resulting structure is finally compacted under heat.
The disadvantage with this method is that it does not allow an equidistant disposition of the fibres in the material due to the need to carry out two inclined plasma depositions for each fibre layer in order that the metallic matrix is able to fill in the gaps between the turns of the wound fibre, and then a third plasma deposition in a radial direction relative to the former in order to cover the fibre layer with metallic matrix material before winding-on the next layer of fibre. Defects in parallelism are observed, and also a lack of uniformity in thickness between successive layers. The method is difficult to perform.
A second known method, in addition to winding fibre onto a former, comprises applying to each wound layer of fibre a sheet of the metallic matrix material. A particular drawback of this method is the risk of not having the fibres in each layer equidistant, due to the fact that the wound-on fibres tend to slip in respect of one another. Further drawbacks are the risk of the sheet of matrix material becoming creased, the risk of not uniformly covering the fibres of each layer, and the difficulty of producing satisfactory successive stackings and correct junctions at the ends of the sheets. Furthermore, the structure of the end product, after compaction of the fibre and sheet stack under heat, incorporates localised stress concentrations which adversely affect the satisfactory life of the product in the severe environments for which it is intended.